This invention relates to treating hard tissues such as tooth enamel or dentin.
Dental compositions such as composites, sealants, and cements generally will not bond sufficiently to tooth enamel or dentin unless the enamel or dentin is pre-treated with an adhesive layer. Typically, the enamel is etched with an acidic solution, followed by application of an unfilled methacrylate-based pre-adhesive composition that is polymerized using a thermally or photochemically activated free radical initiator system to form a layer of adhesive. The dental composition, which is typically a filled methacrylate-based composition, is then placed over the adhesive and polymerized using a free radical initiator system to form a hard, wear-resistant material. The adhesive, therefore, bonds to both the acid-etched tooth and to the dental composition.
Methacrylate-based dental compositions exhibit a relatively high degree of volumetric shrinkage upon polymerization. Accordingly, cationically curable compositions, and hybrid compositions featuring both cationically and free radically curable components, have been suggested as alternatives. Such compositions, which typically include epoxy resins as the cationically curable component, exhibit less shrinkage upon cure than the methacrylate-based compositions.